BAEL-2303 Updated the code as per the review comments.

core-java-8/src/test/java/com/baeldung/reduceIfelse/CalculatorUnitTest.java

@@ -0,0 +1,32 @@
+package com.baeldung.reduceIfelse;
+
+import com.baeldung.reducingIfElse.AddCommand;
+import com.baeldung.reducingIfElse.Calculator;
+import com.baeldung.reducingIfElse.Operator;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class CalculatorUnitTest {
+
+    @Test
+    public void whenCalculateUsingStringOperator_thenReturnCorrectResult() {
+        Calculator calculator = new Calculator();
+        int result = calculator.calculate(3, 4, "add");
+        assertEquals(7, result);
+    }
+
+    @Test
+    public void whenCalculateUsingEnumOperator_thenReturnCorrectResult() {
+        Calculator calculator = new Calculator();
+        int result = calculator.calculate(3, 4, Operator.valueOf("ADD"));
+        assertEquals(7, result);
+    }
+
+    @Test
+    public void whenCalculateUsingCommand_thenReturnCorrectResult() {
+        Calculator calculator = new Calculator();
+        int result = calculator.calculate(new AddCommand(3, 7));
+        assertEquals(10, result);
+    }
+}

core-java-8/src/test/java/com/baeldung/reduceIfelse/RuleEngineUnitTest.java

@@ -2,12 +2,10 @@ package com.baeldung.reduceIfelse;
 
 import com.baeldung.reducingIfElse.Expression;
 import com.baeldung.reducingIfElse.Operator;
-import com.baeldung.reducingIfElse.Rule;
+import com.baeldung.reducingIfElse.Result;
 import com.baeldung.reducingIfElse.RuleEngine;
 import org.junit.Test;
 
-import java.util.List;
-
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotNull;
 
@@ -17,11 +15,9 @@ public class RuleEngineUnitTest {
     public void whenNumbersGivenToRuleEngine_thenReturnCorrectResult() {
         Expression expression = new Expression(5, 5, Operator.ADD);
         RuleEngine engine = new RuleEngine();
-        List<Rule> rules = engine.process(expression);
+        Result result = engine.process(expression);
 
-        assertNotNull(rules);
-        assertEquals(1, rules.size());
-        assertEquals(10, rules.get(0)
-            .getResult());
+        assertNotNull(result);
+        assertEquals(10, result.getValue());
     }
 }